How to attach a side bar with cluster labels to a heatmap (pheatmap). Just a little snippet.

cluster_sidebar.R

library(pheatmap)

# We need to use cutree inside pheatmap()
# functio, capture the returned object into a variable,
# and than extract the tree, cut it again to the same
# number of clusters and reorder.
# Resulting vector is converted to factor and used in the annotation data frame 
# to create cluster labels

x <- some_matrix # matrix to cluster and show as a heatmap 
annot_df <- some_annotation_data_frame # annotation data frame (optional)
out <- pheatmap(x, cluster_rows = T, cluster_cols = F, 
          clustering_method = "mcquitty", clustering_distance_cols = "euclidean",
          clustering_distance_rows = "euclidean",  
          show_rownames = T, 
          annotation_col = annot_df, scale = "row", show_colnames = F, 
          cutree_rows = 4)
clusters <- cutree(out$tree_row, k=4)[out$tree_row[["order"]]]
annot_row <- data.frame(row.names = names(clusters),
                        cluster = as.factor(clusters))
pheatmap(clr_diff, cluster_rows = T, cluster_cols = F, 
            clustering_method = "mcquitty", 
            clustering_distance_rows = "euclidean",  
            show_rownames = T, 
            annotation_col = annot_df, scale = "row", show_colnames = F, 
            cutree_rows = 4, annotation_row = annot_row)